1. Field of the Invention
The present invention relates to (i) positioning devices and more particularly to manually actuated linear stages; and to (ii) anti-backlash screw-nut assembly mechanisms generally used in positioning devices.
2. Description of the Relevant Art
In a linear stage two plates slide parallel and opposite to one another. If a screw and nut assembly connects the two plates of said linear stage, the rotation of the screw generates a rectilinear motion. There is always a tradeoff between the resolution and the total travel of a linear stage, particularly when it is manually operated. For instance, for a screw with a thread pitch of 0.050 inches (1.27 mm), as in a ¼″-20 ACME thread lead-screw, a 5 degree rotation translates into a linear motion of approximately 0.0007 inches (0.0176 mm or 17.6 microns). Using the same lead-screw, it takes 200 full turns or revolutions to move the stage 10 inches (254 mm). This is inconvenient when high resolution and fast motion are required in manually operated single or multi axis positioning devices. However, this limitation can be overcome by temporally disconnecting the threads of the nut and the screw, leaving the linear stage free to be rapidly positioned, and then, re-connecting the threads of the nut and the screw to resume the linear stage high resolution motion.